1. Field of the Invention
The Invention lies in the field of medical technology and relates to an implant that is implanted in human or animal bone tissue or in bone tissue supplemented with bone substitute material.
2. Description of Related Art
The implant according to the invention is, for example, a dental implant that, assuming the function of a natural tooth root, is implanted into a jawbone. In order to permit fastening of an artificial tooth crown, a bridge, or a dental prosthesis, the dental implant comprises, at its proximal end, a fixation location that, after implantation, is located in the region of the bone surface. The dental implant may represent a complete tooth replacement, that is to say may also have a crown region in addition to a root region to be implanted. The implant may also have a different function and may be suitable for implantation in another human or animal bone. Generally speaking, the implant serves for connecting a bone part with another tissue part, in particular with another bone part, or with an artificial part, which artificial part may support or replace a bone part (e.g., artificial joint) or a tooth or it may be a therapeutic auxiliary device (e.g., drug release device, drainage device, or stimulating device for electric or chemical stimulation). The implant may further be such therapeutic auxiliary device itself or it may serve for replacing missing bone tissue or possibly bone tissue to be regenerated (e.g. after removal of a tumor) or it may be an augmentation element for augmenting natural bone in a desired way.
Fixation of tooth replacement structures (individual teeth, groups of teeth, part-prostheses, or complete prostheses) based on the above mentioned dental implants with fixation locations is, according to the state of the art, realized in the following steps: after removal of the natural tooth root one waits until naturally regenerated bone tissue fills the opening in the jawbone. In the region of the regenerated bone tissue an opening adapted to the implant is created. The implant is positioned in the opening, wherein the opening is deep enough for housing the complete implant, which therefore does not protrude beyond the opening. An inner thread defining the fixation location at the proximal face of the implant is closed with a cover screw. The gum is closed over the cover screw and one waits until the bone tissue has ingrown with the implant and by way of this has a stability (secondary stability) sufficient for the loading to be expected. Then; in a further step, the gum is opened over the implant and the cover screw is replaced by a spacer, wherein the spacer projects beyond the gum. Only when the gum around the spacer is healed is the tooth replacement structure fastened on the implant. The briefly described procedure entails a treatment duration of twelve to eighteen months for the patient, of which two to three months fall in the time between the implantation and a point in time at which the bone tissue has grown around the implant or the implant is ingrown in the bone tissue such that the implant has sufficient stability for loading.
The first waiting period (regeneration of bone tissue in an opening in the jawbone) may be avoided or shortened if implants are used which in their shape are adapted as exactly as possible to the original opening, as for example described in the publication U.S. Pat. No. 6,132,214 (Suhonen et al.).
The dental implants according to the state of the art usually consist of pure titanium or of a titanium alloy. These materials exhibit a very good biological compatibility and there are various known surface designs that further improve osseointegration. Very often the implants also comprise macroscopic structures that permit the bone tissue to grow into or through the implant. However, the stability of these known dental implants is only adequate for full loading after complete osseointegration, i.e. only when they are intimately grown around by bone tissue or ingrown or intergrown with bone tissue (secondary stability). In osteoporotic or soft bone, as well as in poorly regenerating bone tissue, for example of older patients it may happen that no sufficient implant stability can be achieved.
The primary stability of the above-described dental implants, i.e. their stability directly after implantation, is greatly limited. For this reason the above mentioned waiting time is added between implantation and further build up. The primary stability of the mentioned implants varies according to implant form, but in most cases it is not sufficient for full loading. Pin-like implants with a thread are restrictedly loadable by tension and compression and possibly transverse forces, in particular when implanted such that at least one thread convolution lies in the region of the cortical part of the bone. They can hardly be loaded by torsion. Implants that do not have a round cross section, i.e. which are adapted to a natural tooth root, are more stable when loaded by torsion, but less stable when loaded by tension. The same applies to plate-like dental implants that may also comprise a plurality of fixation locations.
The un-sufficient loadability of known dental implants would, on loading immediately after implantation lead to movements between implant and bone tissue great enough for impeding or even preventing osseo-integration. However, immediate loading of implants is not only desirable in order to shorten the treatment duration, but also to avoid atrophy of the jawbone due to non-loading, i.e. to promote osseo-integration by way of micro-movements (not exceeding a physiological measure) between implant and bone tissue, which can only be achieved by loading a stable implant.
The primary stability, in particular the ability to be loaded in tension and compression is increased for pin-like implants according to the state of the art by way of a suitably formed threads (U.S. Pat. No. 3,499,222), by spread-out elements (e.g. U.S. Pat. No. 5,766,009, EP-1184006) or by collar-like elements. Anchor-like implants in particular used for fastening wires or sutures are equipped with barb-like surface structures (U.S. Pat. No. 4,360,343) for increasing the primary and secondary stability regarding tension loading. However, these improvements neither permit loading of the implants directly after implantation.